Why Air Filters ???

� Protection to Air Handler components like coil, fan etc.

� To get minimum required indoor air quality.

� To act as guard filters to high efficiency filters.

� To attain required cleanliness for process needs.

� Special filteration needs such as Gas, Odour, VOCs, Smoke, Bacterias etc.

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Weight Arrestance Test

� A weight arrestance test measures how much dust has been

removed by a filter at replacement, by weight.

� The test is misleading, however, because it reveals how well a filter will remove only large and heavy particles, not the smaller particles found in common dust.

� The results of this test are the ones most likely to be used in marketing claims that a given filter has 80% or greater efficiency.

� Removing 80% of the large particles is relatively easy but does little to protect human health or equipment life.

� To demonstrate how ineffective such a test is, try pouring table salt through a standard panel filter with a weight arrestance rating of 80% or greater. Be prepared to clean the floor, since the salt will pass freely through the filter.

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Atmospheric-Dust-Spot Test

� The Atmospheric Dust Spot test utilizes optical targets and atmospheric air to determine how many smudge causing particles pass through a filter. Two targets are compared for discoloration by particles. One target is up stream and one down stream of the filter. The ratio of the discoloration is rated in percent efficiency.

� This test is more accurate than arrestance because a 10-micron dust particle makes about the same size impact mark as a 1-micron particle.

� An atmospheric-dust-spot test is more useful than a weight arrestance test because it measures a filter's ability to capture particles between 0.3 and 6 microns (µ) in size.

� It has one flaw. The atmospheric dust in say New York City has different dust make up than atmospheric dust from Seattle Washington. Test air that has a lower percentage of small particles will allow a filter to have a higher rating.

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DOP Efficiency

� This test is very accurate. It is a test that counts the number of particles that are 0.3 microns up stream and down stream of the filter. If 1000 particles are on the upstream side and 1 particle is on the down stream side the filter has removed 99.9 percent of the particles and it is given a rating of 99.9 % efficient.

� A material called dioctyl phthalate produces smoke with particles that average 0.27 microns in diameter.

� This is the test that is used to rate a High Efficiency Particulate Arrestance, HEPA, filter. For a filter to be called a HEPA it should removed 99% or more of 0.3 micron particles.

� In order to assure that factory tested HEPA filters do not have pin-hole “leaks” and that gasketing and frames are leak free, in-place testing with heterogeneous (cod) dioctyl phthalate (DOP) or suitable substitute is highly recommended. This process introduces cold DOP upstream at a concentration of 10-29 micrograms/liter of air and utilizes a forward light scattering photometer to scan downstream to detect leaks greater than 0.01% of upstream concentration.

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Particle Size Efficiency

• This test will be used when ASHRAE 52.2 is adopted. It is

very similar to the DOP test but measures several particle

diameters not just 0.3 micron. It will be a very true

comparison of how different filters perform.

� Since there are many sized particles, the standard groups sizes together in ranges to make comparison easier. These ranges are then used to give Minimum Efficiency Ratings, MER. of 1 to 16.

� MER of 1 being the least efficient and MER of 16 the most efficient.

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Air Filter MERV Determination

• The MERV rating of an air filter or other air cleaning device is ascertained by using the ASHRAE Standard 52.2 Test Procedure.

• The process involves injection of an aerosol challenge (containing particles in 12 different known size ranges) into an air stream that passes through the air filter under test. Airborne particle counts are then recorded for each particle size, both upstream and downstream of the air filter in order to determine how efficiently the air filter filters out the particles.

• This test is repeated 6 times for each particle size, with the results stated as a filtration efficiency ratio of the downstream to upstream particle count. The lowest values over the six test cycles are then used to determine the Composite Minimum Efficiency Curve for that air filter.

• Once these values are compiled, the 12 size ranges are distributed into 3 larger groups called E-1, E-2 and E-3. Averaging the Composite Minimum Efficiency for each group will calculate the average Particle Size Efficiency (PSE) of the air filter, and the resulting percentages are used to determine the MERV rating.

• The MERV rating is a number from 1-16, stated along with air velocity at which the test was performed, to simplify the evaluation of an air filter using this test method. Higher MERV rating equates to higher air filtration efficiency.

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MERV – Minimum Efficiency Reporting Value

MERV - Air Filter MERV or Minimum Efficiency Reporting Value is an expression of the filtering efficiency of an air filter that has been evaluated using the ASHRAE Standard 52.2 Test Procedure. An air filters performance is determined by comparing airborne particle counts upstream and downstream of the air

filter (or other air cleaning device) under test.

MERV Std. 52.2 1-4 5-8 9-12 13-16 17-20

99.97%

99.99%100.00%

Average

Arrestance

ASHRAE Std.

52.1 60 to 80% 80 to 95% >95 to 98% 98 to 99% N/A

Particle Size

Ranges >10.0 microns 3.0-10.0 microns 1.0-3.0 microns 0.30-1.0 microns

E211 E212 E213 E214 E215 E216

E221 E222 E223 E224 E225 E226

E231 E232 E233 E234 E235 E236

E241 E242 E243 E244 E245 E246

E111 E112 E113 E114 E115 E116

E111 E112 E113 E114 E115 E116

E111 E112 E113 E114 E115 E116

E111 E112 E113 E114 E115 E116

E11Min

E12Min

E13Min

E14Min

E21Min

E22Min

E23Min

E24Min

E31Min

E32Min

E33Min

E34Min

E1avg

E2avg

E3avg

AEROSOL GENERATOR

MERV Calculation

E2

1.00−1.30

1.30−1.60

1.60−2.20

2.20−3.00

E3

3.00−4.00

4.00−5.50

5.50−7.00

7.00−10.00

E111 E112 E113 E114 E115 E116

E121 E122 E123 E124 E125 E126

E131 E132 E133 E134 E135 E136

E141 E142 E143 E144 E145 E146

E1

0.30−0.40

0.40−0.55

0.55−0.70

0.70−1.00

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Air Filter MERV v/s. Efficiency

E1 E2 E3

0.3 to1 mic 1 to 3 mic 3 to 10 mic

MERV 1

MERV 2

MERV 3

MERV 4

G3 MERV 5 20-35%MERV 6 35-40%MERV 7 50-70%MERV 8 > 70%MERV 9 < 50% > 85%MERV 10 50-65% > 85%

F5/F6 MERV 11 65-80% > 85%F6 MERV 12 > 80% > 90%F7 MERV 13 < 75% > 90% > 90%

F7/F8 MERV 14 75-85% > 90% > 90%F8/F9 MERV 15 85-95% > 90% > 90%

F9 MERV 16 > 95% > 95% > 95%

Rating

G2

G4

F5

< 20%

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Understanding Air Filters Rating

• Air filter manufactures rate their products according to standards established by the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE), which uses two different methods for describing filtration efficiency Test 52.2 and Test 52.1. A third test, referred to as a dust spot test is:

� Standard 52.2-1999: This system quantifies air filtration efficiency against particle size ranges: 3 to 10 microns, 1 to 3 microns, and 0.3 to 1 micron. Particle size efficiency is further expressed based on a Minimum Efficiency Reporting Value (MERV) between 1 and 16. A higher MERV indicates greater filter efficiency and one that is more effective against smaller particles. The 52.2-1999 system is a newer approach which is more descriptive.

� Standard 52.1-1992: This system quantifies air filter efficiency in terms of mass of particles removed or 'arrestance'. The 52-1 method is also called a weight-arrestance test. Weight-arrestance tests are misleading because they tell only how well a filter will remove relatively large particles but not the smaller particles typically found in dust.

A third test, which is actually part of the 52.1 is called an 'atmospheric-dust-spot test'. A dust-spot test is more useful than weight arrestance because it measures a filter's ability to capture particles within a given range, usually between 0.3 and 6 micron.

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Average Arrestance by Standard 52.1

Filters with an efficiency of less than 20% in E3 (MERV 1 through MERV 4) must be tested per the arrestance test of ASHRAE Standard 52.1

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Attempt to combine Testing Standrds Type

Eurove

nt

Class

CEN

EN779

Class

ASHRAE 52.1ASHRAE

52.2

EU1 G1

Standard Test Air Flow Rates

The Minimum Efficiency Reporting Value (MERV) must be stated with the air velocity at which the filter was tested. For example, if the filter was tested with an air velocity of 492 FPM and was found to be MERV 10, the filter’s Minimum Efficiency Reporting Value would be MERV 10 @ 492 FPM. ASHRAE Standard 52.2 tests are to be conducted at one of seven airflow rates:

118 FPM (0.60 m/s)246 FPM (1.25 m/s)295 FPM (1.50 m/s)374 FPM (1.90 m/s)492 FPM (2.50 m/s)630 FPM (3.20 m/s)748 FPM (3.80 m/s)

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ASHRAE Standard 62-2001 Ventilation for acceptable IAQ

Air Cleaning Specification

• Specify that filters with a MERV Rating of not less than 6 be installed upstream of all cooling coils.

• Specifies that gas phase adsorbers (typically activated carbon) be used to control gaseous contaminants when needed to provide an adequate level of indoor air quality.

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Filters and Pressure Drop

• Most forced-air systems have a filter located in the return ductwork to remove airborne contaminants before they reach the air handler. However, the filter restricts the flow of air, creating an additional pressure drop in the system that the air handler must then overcome.

• In general, the more efficient the filter is at removing particles, the greater its resistance to air flow, and the greater the pressure drop it creates (for filters of the same cross-sectional area). If the increase in pressure drop is too great, it can reduce energy efficiency, damage the equipment, and increase duct leakage at unsealed seams. Therefore, the filter's function of removing contaminants must be balanced against the additional pressure drop it creates. One way to get good filtration without a lot of pressure drop is to increase the filter area.

• The pressure drop that a filter or other type of air cleaner creates in a forced-air system changes over time. As particles accumulate, they reduce air flow, which increases the pressure drop. Following recommended maintenance schedules is critical to keeping the pressure drop at an acceptable level.

• For typical residential forced-air systems, the increase in pressure drop across the filter, from the time when it is first installed to the time when it should be cleaned or replaced, should be less than 0.5 inches of water gauge (about 125 Pascals). If a filter will create a greater change in pressure drop than this, then a stronger blower and special ductwork design may be required.

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Fan Power Savings

An Illustration – For a 10,000 cfm system, If prefilter pressure drop increases by merely 0.25”wg. For

a Fan eff of 60% and Motor eff of 80%. Also for 6000 hrs/yr and power cost Rs. 7/- per kwh.

• Fan hphpf = Q x (p1-p2) / 6356xEf = 10000x0.25/6356x0.6 = 0.66

• Motor hp

hpm = hpf / Em = 0.66/0.8 = 0.82

• Annual Power Cost

C = Q x (p1-p2)Xhrsxrate / 8520xEf‘xEm‘

= 10000x0.25x6000x7/8520x0.5x0.75

= 32,864.00

• Filter Cost = Rs. 3000.00

• Pay Back = Approx. 33 days

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Comparision between 52.2 and 51.1 Rating Systems

MERV

3 - 10

micron

1 - 3

micron

0.3 - 1

micron

Arrestanc

e Dust Spot Dust spot

1 90% >80% - >98% 70-75%

13 >90% >90% 98% 80-90%

14 >90% >90% 75-85% >98% 90-95%

15 >90% >90% 85-95% >98% ~95%

16 >95% >95% >95% >98% >95%

17* >99% >99% >99% - >99%

18* >99% >99% >99% - >99%

19* >99% >99% >99% - >99%

20* >99% >99% >99% - >99%

1.0-3.0

micron

0.3-1.0

micron

0.3-1.0

micron

ASHRAE 52.2 ASHRAE 52.1

>10

micron

3.0-10

mtcron

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Filter Application

MERV Application

1-4

minimum residential, minimum

commercial, equipment protection

5-8

commercial, industrial, better

residential, paint booth, finishing

9-12

better commercial, better industrial,

superior residential

13-16

health care, general surgery, superior

commercial, smoke removal

17-20*

clean rooms, high risk surgery,

hazardous materials

* = reserved for future classifications

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Filter Application Guide

MERV

Std 52.2

Average

ASHRAE

Dust Spot

Efficiency

Std 52.1

Average

ASHRAE

Arrestanc

e Std 52.1

Particle

Size

Ranges Typical Applications Typical Filter Type

1-4 10.0

µm

Residential / Minimum

Light / Commercial

Minimum / Equipment

Protection

Permanent / Self Charging

(passive) Washable / Metal,

Foam / Synthetics

Disposable Panels

Fiberglass / Synthetics

5-8

95 to98%

1.0 - 3.0

µm

Superior / Residential

Better / Industrial

Workplaces Better /

Commercial Buildings

Non-Supported / Bag Rigid

Box Rigid Cell / Cartridge

13-16

80 to 95%

+

>98 to

99%

0.30 -

1.0 µm

Smoke Removal General

Surgery Hospitals &

Health Care Superior /

Commercial Buildings

Rigid Cell / Cartridge Rigid

Box Non-Supported / Bag99.97

99.99

99.99917-201

N/A

£ 0.30

µm

Clean Rooms High Risk

Surgery Hazardous

Materials

N ote:   T his table is intended to be a gener al guide to filter use and does not addr ess specific

applications or indiv idual filter perfor mance in a giv en application.  R efer to manufacturer (1)  R eser v ed for futur e c lassifications

(2)  D O P E ffic iency

HEPA ULPA

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MERV v/s. Efficiency v/s. Pr. Drop

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Final Pressure Drop

Final resistance must be at least twice the initial resistance at the test airflow rate.

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Relationship between cost and life

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Air Contaminant Size

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Filtration Mechanism

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Fractional Collection Eff v/s. Particle dia

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Dust Holding Capacity

“ The total weight in grams of ASHRAE dust caught by the filter before reaching a pre-determined pressure drop at a given rate of flow”.

Components of ASHRAE Dust (by weight)

72% - Standardized Air Cleaner Test Dust, Fine

(Mean Particle Size – 7.7 microns)

23% - Powdered Carbon

5% - #7 Cotton Linters

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UL-900-Air Filter Flammability Standard

• Class 1 Air Filters� Those that, when clean, do not contribute fuel when attacked by

flame and emit only negligible amounts of smoke.- shall not produce flame or sparks when subjected to the UL Flame-Exposure Test.

During the flame-exposure test, the Class 1 air filter shall not cause the development of an area of more than 16.1 cm2 (approx. 2.5 sq.in.) as measured below the smoke-density time curve. Additionally, when subjected to the UL Spot Flame Test, the upstream face of a Class 1 air filter shall not continue to flame after removal of the test flame.

• Class 2 Air Filters� Those that, when clean, burn moderately when attacked by flame

or emit moderate amounts of smoke, or both- shall not produce flame or extensive (25 or more) sparks which are sustained beyond

the end of the test duct when subjected to the flame-exposure test, and shall not cause the development of an area of more than 58cm2 (approx. 9sq.in.) as measured below the

smoke density time curve.- Adhesive Material- used for coating the filter media, or other part of the air filter, shall

have a flash point of not less than 163�C (approx. 325�F) as determined by the Test Method for Flash and Fire Points by Cleveland Open Cup, ASTM D92-1990.

� GENERAL - - shall not contain unbonded asbestos fiber materials.

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Types of HEPA Filters

Method Aerosol Method Aerosol

99.97%*

at 0.3 µm

99.97%

at 0.3 µm

99.99%

at 0.3 µm

100.00%

at 0.3 µm

99.97%

at 0.3 µm100.00%

at 0.1 to 0.2 µm

Comments

Minimum efficiency

rating

A MIL-S TD 282 Thermal DOP None None

Filter

type

Penetration Test Scan Test (see note)

B MIL-S TD 282 Thermal DOP None

C MIL-S TD 282 Thermal DOP Photometer

Thermal DOP Photometer

None Two flow leak test

Polydisperse DOP

Polydisperse DOP

E

MIL-S TD 51477 or

MIL-S TD F51068 Thermal DOP Photometer Polydisperse DOP Two flow leak test

D MIL-S TD 282

OpenF IE S -RP CC 007 Open

P article

C ounter

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Standard s comparision

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